Centrifugal switch with fluent conductor for rotating projectiles



Aug. 25, 1959 s. M. DARR 2,901,569

CENTRIFUGAL SWITCH WITH FLUENT CONDUCTOR FOR ROTATING PROJECTILES Filed Sept. 19, 1945 IIIIIJ INVENTOR SAMUEL BARR Patented Aug. 25, 1959 ice CENTRIFUGAL SWITCH WITH FLUENT CGN- DUCTOR FOR ROTATBNG PROJECTILES Samuel M. Darr, Silver Spring, Md., assignor to the United States of America as represented by the Secretary of the Navy Application September 19, 1945, Serial No. 617,366

9 Claims. (4:1. 102-40) This invention relates generally to centrifugally operated fluent conductor containing control devices and more particularly to an improved mercury electric switch structure of the type adapted to be installed in projectiles of the rotating type and which functions to open an electrical circuit under the effect of centrifugal force developed by projectile spin.

Prior-art devices of the general class under consideration usually comprise a body structure having intercommunicating chambers therein: a pressure chamber in which a conductive fluid, such as mercury, is normally confined in contact with two conducitve members to complete an electric circuit between them, and a sump chamber for collecting the conductive fluid when it flows, under the influence of centrifugal force, through a layer of porous material, such as blotting paper, interposed between the two chambers, thus depressing the fluid level below the point of contact with one of the conductive members and breaking the circuit. The porous material offers suflicient resistance to the mercury to prevent its passage therethrough except under the considerable force developed by spin. It has been found, however, that when a single-layer porous diaphragm of blotting or filter paper is used, non-unifomity of the porosity of the sheets of material from which the diaphragms are made results in wide and highly undesirable variances in the rates of fluid flow as between different units. It has thus been found difficult to produce such units in quantity without excessive reject wastage due to the above-mentioned nonuniformity. It is an object of the present invention to provide switches of the indicated character but which do not incorporate filter paper, which are so designed as to be rapidly and economically manufacturable on a production basis, and which may be relied upon to conform accurately to critical requirements, such as the opening of an electrical circuit after a predetermined time delay.

In some prior-art switches, the flow of mercury to the sump chamber is accompanied by a decrease in pressure below atmosphere in the pressure chamber which tends to retard open circuiting of the switch. This diificulty in the present invention is eliminated by the provision of an air channel or duct between the chambers. However, this expedient has heretofore involved relatively complicated mechanical structures and designs for preventing the passage of mercury through the air pressure-equalizing channel.

It is an object of the present invention to avoid the above-mentioned disadvantages and the limitations of prior-art devices by providing a relatively simple liquidcontaining control device, the fluid-flow rate of which may be predetermined with a reasonable degree of accuracy.

The invention itself, both as to its organization and method of operation, together with other and further objects and advantages and novel features believed to be characteristic thereof will best be understood by reference to the following specification taken in conjunction with the accompanying drawings, in which: Fig. 1

is a plan view of a preferred embodiment of the electrical switch, in accordance with the present invention; and Fig. 2 is a longitudinal sectional view on line 22 of Fig. 1.

In accordance with the invention, the control device comprises an exterior casing which is provided with an interior flow-regulating cup, forming a chamber containing a fixed contact, which chamber contains a fluent conductor operating as a movable contact. The cup and casing cooperate to form a spaced sump. Under centrifugal force, the fluent conductor flows from the chamber through the base of the cup, which forms a partition into the sump. The switch is so installed in a projectile that, due to deceleration of the projectile during flight, this flow is in the direction of a skewed curve through the partition or base of the cup, and the pressure differential thus created by creep permits escape of displaced air through the side wall of the cup from the sump to the contact chamber.

Referring now particularly to Fig. 2 of the drawing, the electric switch there illustrated is a liquid-containing control device adapted to be operated by the flow of mercury in the general direction indicated by the arrow B. This flow is caused by centrifugal force developed as a result of the revolution of the switch as a unit about a projectile spin axis indicated by arrow A, which axis is located externally of the switch, at right angles to the longitudinal axis thereof and proximate to the inner fixed contact shown and hereinafter described. The switch is adapted to be installed transversely in a projectile. Two conductive strips l1 and 12 individually connect the switch contacts to the external circuit. In the embodiment shown, the circuit is adapted to be opened by operation of the switch for the purpose, for example, of breaking a protective short circuit across a firing squib. It will be recognized, however, that the switch is equally adaptable to other uses, and may readily be employed either to close or to open an extenral circuit. Strip 11 terminates in an exterior collar 13, electrically and mechanically connected by spot welding generally indicated at 14 to a conductive metallic sheet metal casing 15, which case constitutes the main housing member of the switch. Casing i5 is generally cylindrical in shape and formed with a reduced, closed outer end forming an interior annular shoulder 16 and a sump 17.

The shoulder 1.6, which is disposed between the two interior chambers of the shell, forms a seat to receive and retain a molded sintered metal flow-regulating cup 18, nested within shell 15. End wall 19 of the cup constitutes a porous flow-delaying partition between the interior cup pressure chamber 20 and the sump chamber 17. Chamber 2% contains a suitable quantity of mercury, which mercury functions as a movable circuit electrode.

The cup is made of material permeable to mercury. Since pure nickel is not amalgamated by mercury, nor susceptible to substantial corrosion, the cup is preferably constructed of molded sintered nickel.

Cups of this type are capable of mass production, in lots or quantities of varying porosity or degrees of permeability. The cups in each lot maintain a high degree of uniformity in porosity and the different lots may readily be identified as to their timing characteristics. The cups may be manufactured with facility; they possess an internal resistance that does not substantially change during projectile flight; and they may, with convenience, be assembled and incorporated in the switch structure. The use of this type of cup insures a relatively high factor of safety against accidental displacement of components of the switch.

The other contact comprises a conductive member 22, having a reduced shank portion 23 rigidly secured in coaxial rclationship with respect to the casing and insulated therefrom by washers 24 and 25, washer 24 hearing on an annular shoulder of conductive member 22 and on one end of cup 18, and washer 25 being compressed by a rolled annula flange-. 26 on a ing 5. The cir u f om strip lite-c n uctive num er 22 is mplet d y p sitic i z ig c 1a 2 of st ip 2 ts eerie reli flanged portion 29 of member 22 and washer 3%, which bears wi h c mpress on ainst c l r nd Washer .25.

Coming now to a description of the operation of the 99 3191 de icehereinabove described, it will first be assumerl that the mercury has a closed-circuit relationship respect to contact member 22, that is, that the level of the mercury within cup 18 is such that the surface of tbe mercury contact with contact member 22. Under such an a sumed on i ion, the confining p P en s thefluid'fr'orn flowing out of the pressure chamber. It be seen that if the switch is installed in a projectile, it may be utilized in this condition to short-circuit a firing squib and thus to prevent firing of the projectile un il t h s le t t e su 7 While the projectile is in flight, so that the switch is revolving about axis A, centrifugal force tends to pull mercury outwardly from chamber 20 to chamber 17. The mercury flows radially and forwardly into sump chamber 17, displacing the contained air. The forward component of flow is caused by creep of the mercury resulting from deceleration of the projectile. Under hydraulic pressure in the sump chamber, air is vented through the rear porous side walls of the cup into chamber .20. The short circuit comprising strip 12, contact 22, the mercury, casing 15, cup 18, and conductive strip .11 is broken when the mercury moves outwardly in the cup to such an extent that the surface of the mercury no longer touches contact 22. The time flow of the mercury may be varied by changing the density or porosity of cup 8.

It is to be understood that the form of the present invention hereinabove shown and described is to be taken as a preferred example of the same and that various changes inthe shapes, sizes, and materials of the several components may be made without departing from the spirit of the invention or the scope of the appended cla ms- What is claimed is:

1. An electrical switch, comprising, confining means,

.a. contact member, .a conductive fluid adapted to have a circuit relationship with respect to said contact member, and flow-restricting means in said confining means for maintaining 'said fluids in one circuit relationship with respect to said contact member under one condition of fluid pressure acting on said confining means, said flowrestricting means comprising a sintered metal cup for permitting said fluid to flow there-through under another condition of said fluid pressure acting on said confining means, thereby to assume a different circuit relation-ship with respect to said contact member. 2,. An electrical switch, comprising, a confining member, .a contact member, a conductive fluid adapted to have a circuit relationship with respect to said contact member, and flow-restricting means for maintaining said ,fluid in closed circuit relationship with respect to said contact member under a given condition of fluid pressur'e..acting on said confining member, said flow-restrict- Wing m ans comprising a sintered metal cup for permitting said fluid to flow therethrough under a condition of greater fluid pressure acting on said confining means, thereby to assume an open circuit relationship with respect to said contact member.

3, An electrical switch of the type adapted for orbital mo ement. about an axis of revolution, comprising, a

. 4 V contact member, a conductive fluid adapted to have a closed circuit relationship with respect to said contact member when in a static condition with respect to said axis of revolution, and flow restricting means surrounding said liquid and including a sintered metal cup for permitting said fluid to flow thcrcthrough under pressure developed by centrifugal force, thereby to assume an open circuit relationship with respect to said Contact member.

4. A centrifugal electric switch, .COmprising, an exterior casing, a sintered metal cup nested within the casing and oop a ing herewith to t m a p s re ham r a a sump chamber, and fixed and fluent contact members normally disposed within said pressure chamber.

5. A centrifugal switch, comprising, an exterior casing having a terminal connection, a sintered metal cup forming a chamber and nested within said casing to define a separate sump within said casing, an end wall assembly closing said chamber and including a terminal connection, a fluent contact within said chamber and a fixed contact mounted in said end wall assembly and protruding into said chamber. 7

6. In a centrifugal switch, the combination with a shell having an interior abutment portion and forming an end sump, of a sintered metal cup having its closed end seated against said abutment and forming a contact chamber, an end wall assembly sealing the open ends of said cup and shell, a fluent conductor contained in said chamber and forming a movable contact, and a fixed contact mounted in said end Wall assembly and protruding into said chamber.

7. In an electric circuit control device, a conducting liquid, said device being adapted to exercise its controlling function by movement of said liquid therewithin, an arrangement for regulating the flow of said liquid therethrough comprising a cup shaped sintered metal member.

8. A centrifugally operated conducting liquid-containing electric circuit control device, comprising, a body structure having intercomrnunicating chambers therein and adapted for orbital movement about an axis of revolution, said chambers being at variant distances from said axis, whereby said liquid in said chamber moving in the minor .orbit tends to flow under the influence of centrifugal force to the chamber moving in said major orbit, and flow-restricting regulating means comprising a sintered metal partition interposed between said chambers,

9. A centrifugally operated conducting liquid-containing electric circuit control device, comprising, a body structure having intercommunicating chambers therein and adapted for orbital movement about an axis of revolution, said chambers being at variant distances from said axis, whereby said liquid in said chamber moving in the 'm-inor orbit tends to flow under the influence of centrifugal force to said chamber moving in the major orbit, flow restrictive sintered metal cup means interposed between said chambers, a part of the last-mentioned means defining a gas pressure equalizing means extending from .said last-named chamber to said first-named chamber proximate to said axis, and a contact carried by the body structure and electrically insulated therefrom for cooperation with said structure and the conducting-liquid in the chamber moving in the minor orbit for closing an electric circuit.

References Cited in the file of this patent UNITED STATES PATENTS 

